BILLINGS (AP) — State officials said Tuesday that they’ll rework plans to ease restrictions on Yellowstone National Park bison that enter Montana, after the Board of Livestock declined to act on a proposal giving the animals more room to roam.

Board members said they wanted more information on the potential costs of the proposal that would allow bison onto more than 400,000 acres west and north of the park, officials said.

That includes Hebgen Lake Basin, the Taylor Fork of the Gallatin River and other areas where bison, also known as buffalo, were long prohibited because of concerns the animals would spread disease to livestock.

Under a 2000 agreement between the state and federal officials, thousands of bison were killed as they attempted to leave the park.

Government policies dictating the capture and slaughter of bison entering Montana were loosened under former Gov. Brian Schweitzer. But resistance to further change runs strong within the livestock industry because of fears about the disease brucellosis.

After the Board of Livestock in January rejected a plan that would have increased tolerance for bison in Montana, the Department of Livestock and Montana Fish, Wildlife and Parks presented the board Tuesday with a revised version linked to population size.

It would have allowed bison to roam outside Yellowstone year-round only if their population were reduced to 3,300 or fewer animals. That’s about 1,300 fewer than the most recent tally taken last summer.

State Veterinarian Marty Zaluski said some board members thought 3,000 was a better level. They also wanted more involvement from the cattle industry and details on how much it would cost to manage the much larger landscape where bison would be allowed.

The population last dropped below 3,000 in 2008, a year when more than 1,600 bison were captured and shipped to slaughter or killed by hunters.

The proposal to expand where bison can go in Montana needs approval from the Board of Livestock and Pat Flowers, the Fish, Wildlife and Parks regional supervisor for southwest Montana.

Flowers said Tuesday the concept remains viable, but there’s still “some work to do” to address the livestock board’s concerns. He added that the costs could turn out to be substantially lower than under current policies, in which a helicopter is periodically used to haze bison back into the park after they leave in the winter.

Biologists say Yellowstone has some of the most genetically pure bison in the world, direct descendants of the few animals that survived the near-extinction of the species last century.

Also Tuesday, park administrators sought the public’s help in identifying who killed three bison inside Yellowstone last week.

The animals were likely shot sometime between the evening of March 13 and the morning of March 15 along a road in the Blacktail Plateau area, administrators said.

Federal law prohibits killing or removing animals from Yellowstone. A reward of up to $5,000 was offered for information leading to the conviction of those responsible.